1. Field of the Invention
This invention relates to a loom, such as an air jet loom. More particularly, it relates to a method and an apparatus for detecting the weft yarn inserted by a jet fluid through a weft yarn guide passage which is provided along the reed.
2. Description of the Prior Art
In a jet loom, wherein the weft yarns are inserted by a jet fluid into the warp shed, the insertion condition of the weft yarns markedly influences the quality of the woven fabric. In the conventional practice shown in FIG. 1, a weft yarn detection unit 2 is provided outside of the trimmed or waste selvage W1 or between the selvage W1 and the woven cloth W in order to determine whether the end of the weft yarn Y impelled from the weft inserting main nozzle has reached the predetermined detection area. This prior-art device is shown for example in the Japanese laid-open patent publication No. 57-5947. In this prior-art device shown for example in FIG. 2 herein, a weft sensor 2 is attached to the front side of the slay 6 and includes at its end a light emitting element 3 and a light receiving element 4 juxtaposed in the direction of the weft guide passage S, and a bar lens 5 ahead of the elements 3, 4. The light projected from the element 3 is condensed by the bar lens 5 and reflected by the weft yarn Y, the reflected light then being condensed by the bar lens 5 and received by the light receiving element 4 for detecting the weft yarn. Thus, the prior-art device aims at improving the weft yarn detection accuracy by increasing the changes in the light volume.
However, when the weft yarn sensor 2 thus aimed at improving the weft yarn detection accuracy is placed outside of the cloth W or the waste selvage W1, as shown in FIG. 1, excess weft yarn must be inserted for assuring a positive weft yarn detection, thus causing wastage of weft yarns to run, counter to the present-day trends towards material saving. In addition, what is called "end failure" that is not abnormal, i.e. the case in which the end of the weft yarn Y does not reach the location of the weft sensor 2 but regular weaving is still achieved, is also regarded by the detector as a failure in weft insertion, so that loom operation is automatically halted. Such needless interruption of the loom operation is not desirable since the operational efficiency of the loom is thereby lowered, while the rate of occurrence of the weaving bar at the time of the halting and starting of the loom is increased, thus adversely affecting the quality of the woven cloth.
When the weft yarn sensor 2 is arranged outside of the woven cloth W, weft yarn detection at an earlier time is not feasible. Thus, the timing of the detection of the failure in weft filling must correspond with the times when weft yarn end reaches the sensor. For example, even in instances wherein the weft yarn end reaches only the half width of the cloth, detection of a failure in weft insertion will be made by the sensor at the time when the weft yarn end is assumed to reach the location of the weft yarn sensor, thus causing delay in sensing the weft yarn insertion error with consequent difficulties in the subsequent control of the loom operation.
For assuring early detection of the weft insertion error, it would be appropriate to position the weft sensor within the extent of the cloth width. However, this has not been feasible with the aforementioned prior-art device since no means are provided to tackle or spread the warp yarns so as to allow insertion of the sensor into the warp shed.
Japanese laid-open patent publication No. 54-240501 shows a weft yarn detection apparatus in which the light emitting section is provided on the top of the reed within the upper region of the warp yarns, and the light receiving section is provided in the lower region of the warp yarns so that the projected light may be received by the light receiving element in the lower region of the warp yarns to permit weft yarn detection within the extent of the cloth width. However, a positive yarn detection is not possible with the prior-art system designed to sense one weft yarn by using projected light adapted to traverse the densely arranged warp yarns, and the accuracy in weft yarn detection achievable with the prior-art system is usually low.